Thank you for reaching out to us through the Community. I am sorry to hear that you experienced this issue. It is possible to retrieve the contacts if they were on a specific list that you had emailed a campaign in the past. In order to locate the contacts, you would click on the "Reporting" tab located at the top of your navigation toolbar. Then, scroll down until you see the title of a specific campaign that you sent to that list. Click on the "Sent" number of contacts for that campaign. Once you have done that, you should be able to select the contacts that were removed and export them out to a spreadsheet which you can use to import them back in. I hope this helps. Let us know if you have any additional questions.
We're glad Lucas was able to help you! Please reach out if you have any other questions. We're happy to help!